Optoelectronic modules are used in, for example, telecommunication systems. Optoelectronic modules frequently include a semiconductor laser mounted on a rigid substrate within a hermetically sealed housing. A circuit containing various circuit elements such as resistors, inductors, thermistors, capacitors, transistors, etc, may also be located on the substrate within the housing. The circuit is frequently coupled to an external control circuit via control lines. The control circuit sends electrical control signals into the module and senses signals from inside the module (e.g., temperature from a thermistor or transmitted power from a monitor photo diode (MPD)). The internal circuit is responsive to the control signals to regulate the operation of the laser to cause the laser to output a desired light pattern. In addition, the light output by the laser may be modulated to develop a desired communication signal.
One or more optical fibers are typically optically coupled to the laser through one or more walls of the housing. The optical fiber(s) carry the output signal(s) developed by the laser to an external optical network or the like. The fiber(s) must be carefully aligned with the laser in order to produce output signals of acceptable strength. Indeed, alignment less than a few microns is often desired to optimize the strength of the signals output by the laser.
To couple the output of the laser into the optical fiber(s), the optoelectronic module is typically provided with an optical lens located between the laser and an end of the fiber. The lens and/or the fiber may be mounted on a flexure. A flexure is a resilient metal element with one or more pairs of opposed legs separated by a central mounting area. The lens or fiber is coupled to the central mounting area of the flexure. The vertical position of the lens or fiber can be adjusted by flexing the flexure. Downwardly flexing the flexure causes the legs of the flexure to move outwardly along the substrate. When the desired position is reached, the legs of the flexure are bonded to the substrate to secure the lens or fiber against further vertical movement.
Typically, the desired position of the lens or fiber is determined through an active alignment process. In the active alignment process, the laser is energized to pass light through the lens or fiber. A power meter (PM) or other monitoring device is positioned to monitor the strength of the light signal passing through the lens or fiber. The flexure is then moved to maximize the signal received by the PM. When the lens or fiber is positioned in a vertical location wherein the signal detected by the PM is maximized, the flexure is bonded in place to secure the lens or fiber in that location.
Prior art optoelectronic modules require at least two active alignment procedures during the manufacture process (e.g., one alignment process to align the lens and the laser and one alignment process to align the lens and the fiber). Such procedures are costly in cycle time and labor requirements. Moreover, the narrow tolerances associated with positioning the optical components of the module ensure a fairly high yield loss. Because the modules typically include some very expensive components, a high module fail rate translates into high economic loss, which results in an overall increase in the price required to earn a profit from selling such modules. The communications industry, on the other hand, is demanding lower cost optical components.